The present invention relates to a handheld power tool as is known from US 2010/108736 A or US 2004/134961 A, among others. A combustion chamber having a piston is filled with air and a combustible gas. The gas mixture is ignited, whereupon the combustion gases accelerate the piston. The kinetic energy of the piston is used to drive a nail into a workpiece. A piston compressor compresses the air and feeds it into a reservoir. The combustion chamber is fed from the reservoir. The increased air pressure makes it possible to feed the same quantity of air for consumption in a smaller combustion chamber. However, the additional compressor and the energy source required therefor lead to an increased weight and size of the setting tool.